The present invention relates to valves for controlling fluid flow and, more particularly, to a valve that includes a rotatable plug or movable gate which cooperates with at least one pair of seats for controlling and sealing fluid flow.
Known valve designs include a ball or gate that is rotatably or movably mounted in a valve body and that has a through hole through which fluid flow when the hole is aligned with inlet and outlet ports. Such valves are closed when the plug or gate is rotated or moved so that a solid side of the plug or gate entirely blocks the flow path of the inlet port. The plug or gate presses against seats, one positioned on each the upstream and downstream side, which press against the valve body. Typically, the plug or gate has some float so that in a sealing situation the upstream fluid pressure causes the plug or gate to be strongly biased against the downstream seat which, in turn, is biased against the valve body forming a seal therewith.
Under the stop flow condition described above, there is ordinarily a large amount of pressure within the valve cavity which houses the plug or gate and seats because fluid under pressure enters between the plug or gate and seats. The downstream seat is strongly biased against the valve body by the fluid in the flow path which is transmitted by the plug or gate. In the event that fluid pressure is suddenly bled off upstream, the upstream seal formed between the upstream seat and the valve body will have a tendency to trap pressure in the cavity such that resultant pressure force on the upstream side of the upstream seat will cause the upstream seat to be biased against the plug or gate. This trapped pressure condition requires a significantly higher operating torque to rotate the plug or to move the gate and may result in overstress of components if a temperature change occurs while the valve is in this condition.
It is an object of the invention to design a valve that solves the aforementioned problem and, at the same time, provides a reliable seal during any mode of operation, has easily removable parts and is easily serviceable, and comprises components that are easily manufactured.